There are four fire detection loop assemblies in each engine.Each assembly has two detector elements, two gas charged sense tubes and a support tube. One is loop A and the other is loop B. each loop has four detectors.

The detector elements have these components:-

A] Overheat pressure switch.

B] Fire pressure switch.

C] Fault pressure switch.

D] Resistors.

E] Terminal stud.

F] A stainless steel, gas charged tube.

Locations of the Engine detector elements:-Two on the upper fan case section.Two on the lower fan case section.Two on the left core section.Two on the right core section.If one loop fails, the entire loop assembly has to be replaced.

The three pressure switches sense for these conditions:-

Overheat.

Fire.

Fault [loss of gas pressure].

Gas pressure in the sense tube holds the FAULT pressure switch in the normally closed position. The other two pressure switches close when the gas pressure increases because of an overheat or fire condition.The overheat and fire signals go to the Engine and APU fire detection control module. This module supplies overheat or fire indication in the flight compartment.If the pressure in the sense tube decreases, the FAULT switch opens, This causes a large change in resistance which sends the fault signal to the Engine and APU fire detection control module. This module sets the fault condition and the related FAULT AREA light comes on.

The Engine and APU fire detection control module is located in E2-2.

There are five amber FAULT AREA lights on the front of the unit.

Engine 1 has a light for each detector loop.

Engine 2 has a light for each detector loop.

APU has one light for its detector loop.

Three red FAULT DISPLAY lights are below the FAULT AREA lights, these are light emitting diodes [LEDs].The FAULT/INOP TEST switch is below the FAULT DISPLAY placard.Under normal conditions, all front panel lights are off, when a fault condition occurs, the related FAULT AREA light comes on . The FAULT DISPLAY lights show a fault code.

FAULT/INOP TEST:- Press and hold for 5 seconds, Test passes if all 8 lights are on.

The Overheat detector switch on the overhead/fire protection panel lets the crew select the mode of operation.

The APU detector loop has three sense elements. Each element has thee pressure components:-

A] Fire pressure switch.

B] Fault pressure switch.

C] Resistors.

D] Terminal stud.

E] stainless steel gas filled tube.

These are the locations of the three sense elements:-

A] Upper APU compartment.

B] Lower APU compartment

C] Tailpipe.

These are the results of an APU fire condition:-

A] APU fire handle lights come on.

B] APU fire handle unlocks.

C] Aural warning unit gives the bell sound.

D] APU automatic shutdown.

E] APU remote horn and light operate.

These are the flight compartment indications of an APU fire condition:-

A] Fire handle light on P8.

B] Fire warn light on P7.

C] Aural warning unit gives a bell sound.

The APU ground control panel supplies the external indications of an APU fire. A horn and a red light operate on the APU ground control panel. The horn sound and the red light operate alternately at a one time per second rate.

To stop the horn and bell sounds and cause the light to operate continuously push one of these buttons.

A] BELL CUTOUT push-button switch on P8.

B] FIRE WARN lighted push-button switch on P7.

C] HORN CUTOUT push-button switch on P28.

These are the fire extinguishing systems on the airplane:-

A] Engine fire extinguishing system.

B] APU fire extinguishing system.

C] Lavatory fire extinguishing system.

D] Portable fire extinguishers.

These are the components of the Engine fire extinguishing system:-

A] Engine and APU fire control unit.

B] Two fire extinguishing bottles.

C] Engine fire extinguishing ports.

When there is an overheat or fire condition, the fire warning switch for that engine unlocks. You can also use the warning switch override under the handle to unlock the fire warning switch. When you pull the switch up, the engine systems are shutdown and isolated for safety.

When you turn the Engine 1 [left] fire warning switch clockwise, the extinguisher bottle squib 1 on the R bottle operates. This breaks a seal and lets the halon gas in the R bottle to go to engine 1. If you turn the same engine fire warning switch counterclockwise, the extinguisher bottle squib 1 on the L bottle operates. This sends the halon gas in the L bottle to go to engine 1. When an engine fire extinguisher bottle is empty, the related BOTTLE DISCHARGED light on the overheat/fire protection panel comes on.

The Engine 2 [right] fire extinguishing system operates the same as engine 1. The difference is that the engine 2 fire handle switch causes the discharge cartridge 2 on the L or R bottle to operate and break a seal.

B] TEST switch lets you to do two tests. One test is for the fault detection circuits. The other test is for the fire detector loops.

C] OVHT DET switches let you select the mode of operation, loop A or loop B, you may also select NORMAL for both loops.

D] EXT TEST switch lets you do a check of the extinguisher bottle squibs for continuity.

When you pull the switch up, these functions occur:-

A] Engine fuel shut off valve closes.

B] Thrust reverser control power goes off.

C] Spar fuel valve closes.

D] Power to the engine driven pump low pressure warning system goes off.

E] Bleed air valves closes.

F] Hydraulic shut off valve closes.

The fire extinguishing system receives power from the 28vdc hot battery bus.

The Engine and APU fire extinguisher test has these components:-

A] Three position toggle switch, spring loaded to the neutral position.

B] L bottle test light.

C] R bottle test light.

D] APU bottle test light.

When you set the EXT TEST switch to the 1 position, a test of these squibs occurs:-

A] L bottle number 1 squib.

B] R bottle number 1 squib.

C] APU bottle squib.

When you set the EXT TEST switch to the 2 position, a test of these squibs occurs:-

A] L bottle number 2 squib.

B] R bottle number 2 squib.

C] APU bottle squib.

The green test lights come on to show a successful test.

When the EXT TEST is carried out, The voltage regulator in the overhead fire protection panel decreases the voltage to a level that will not cause a squib explosion.

When you operate the APU fire extinguishing system, it fills the APU compartment with halon gas to extinguish the fire.

The APU fire extinguishing system has these components:-

A] Fire Extinguisher bottle.

B] Overheat/Fire protection panel.

C] APU ground control panel.

When there is a fire condition, the APU fire warning switch unlocks, you can also use the warning switch override under the handle to unlock the switch. When you pull the APU fire warning switch up, the APU systems are shutdown and isolated. Turn the APU fire warning switch clockwise or counter-clockwise, this causes the APU fire extinguisher bottle to discharge halon gas. You can also use the APU ground control panel to operate the APU fire extinguisher bottle.

When the APU fire extinguisher bottle is empty, the APU BOTTLE DISCHARGED light on the overheat/fire protection panel comes on.

The APU DET INOP light and MASTER CAUTION lights come on if the APU fire detection circuits do not operate.

The APU extinguisher bottle is spherical in shape. The bottle contains halon under nitrogen pressure of 800 psi at a temperature of 70degF [21degC].

The bottle releases halon when you pull up and turn the APU fire warning switch in any direction. There is a squib explosion, which breaks open a diaphragm on the bottle. The halon gas flows from the bottle to the APU compartment. If the bottle temperature increases to 266 degF [130 degC] or approximately 1800 psi, the safety relief port breaks open. This blows out the disc and discharges the halon into the accessory compartment.

The APU ground control panel on ground gives you visual and aural indications of an APU fire and lets you extinguish it.

The APU ground control panel has these components:-

A] Red fire warning light.

B] Fire horn.

C] Horn cutout switch.

D] APU fire control handle.

E] Bottle discharge switch.

When thee is a fire in the APU, the horn and light operate alternately and the APU stops.

When you push the horn cutout button, the horn sounds stops and the red light stays on continuously.

When you pull the APU fire control handle, the APU system stops and isolates from other systems.

When you pull down the APU fire control handle, you also arm the bottle discharge toggle switch. You push the toggle switch to cause the APU bottle squib explosion.

When you pull the APU fire warning handle switch up, a signal goes to these components:-

The Lower cargo compartment smoke detection system gives a warning in the Flight deck if there is smoke in a lower cargo compartment, The warnings are for the forward and aft cargo compartments.

The Forward lower cargo compartment has four smoke detectors and the aft lower cargo compartment has six. The smoke detectors are in the ceiling of the cargo compartment.

One smoke detector cargo electronics unit is in the ceiling of each cargo compartment inboard of the cargo door.

These are the components in the Flight deck that have an interface with the lower cargo compartment smoke detection system:-

A] Cargo smoke detection and fire suppression module.

B] Aural warning unit.

C] Fire warning lights on P7.

These are the functions of the lower cargo compartment smoke detection components on the cargo smoke detection and fire suppression module:-

A] DETECTOR FAULT amber light is on if one or more of the detectors has a power failure.

B] A three position [A,NORMAL,B] DET SELECTSWITCH, one for each cargo compartment. NORM position lets both detectors or with one detector failed sense smoke and give fire alarm. A or B lets the selected detector sense smoke and give fire alarm.

If the forward cargo compartment with four smoke detectors [2 loop A and 2 loop B], only lights 1A,1B,2A and 2B connect to the smoke detectors. The other lights are active and connect externally by a jumper cable loop.

In the aft cargo compartment with six smoke detectors [3 loop A and 3 loop B], only lights 1A,1B,1C,2A,2B & 2C connect to the smoke detectors. The other lights are active and connect externally by a jumper cable loop.

Smoke detection test [CEU]:-

LAMP TEST:- If any of the 16 red lights do not come on, change the CEU.

PRESS TO TEST:- All 16 red lights come on, test passed. At the same time, on P8-75, 2 EXT FWD, AFT green lights come on, FWD and AFT red switch lights come on, DISCH amber light comes on. If during test, the red light does not come on , change smoke detector or check
Jumper cable. At the same time, on P8-75, the DETECTOR FAULT amber light is on.

If the detector does not operate, the DETECTOR FAULT amber light comes on for a fault indication.

Smoke detection test [P8-75]:-

TEST, 2 EXT FWD, AFT green lights come on, FWD and AFT red switch lights come on, DISCH amber light comes on, FIRE red light come on [P7] and bell rings. At the same time, on CEU, all 16 red lights come on. If FWD or AFT red switch light does not come on select A or B or DET SELECT switch and do the test again. A red light on the CEU not on shows you which detector is failed or a problem with external Jumper loop.

During these tests, the red lights on the CEU are visible through the fiberglass cover.

The lower cargo compartment fire extinguishing bottle is in the air conditioning distribution bay. The bottle is on the left side of the air conditioning mix chamber. It attaches to a bracket on the aft bulkhead.

The bottle has two discharge [squibs] assemblies connected to the discharge tubing. The discharge tubing sends extinguisher to the forward and aft cargo compartments.

C] TEST pushbutton switch, does a test of the extinguishing system and cargo smoke detectors.

D] FWD, AFT green EXT lights are on during the extinguisher test.

Bottle discharge:- Push the forward or aft fire arm switch to arm the cargo fire extinguishing system. Push the cargo fire discharge switch for at least one second. The switch lets power from the hot battery bus go to the bottle forward or aft squib. The bottle discharges extinguishing agent to the affected cargo compartment to provide fire suppression for 60 minutes.

You can do a test of the lower cargo compartment extinguisher bottle discharge squibs and the DISCH amber light. You use a test switch on the cargo smoke detection and fire suppression panel. A test switch on the cargo electronics unit also does a test of these components.

The Lavatory smoke detection system alerts the flight crew to smoke conditions in the lavatories.

A green indicator light comes on when a smoke detector has power. When there is smoke in the lavatory, the detector red alarm indicator light comes on and the detector horn sounds. There is an optional P5 panel smoke light which illuminates.

The smoke detector assembly has these components:-

A] Alarm horn.

B] Alarm indicator.

C] Electrical connector.

D] Power indicator.

E] Interrupt switch.

F] Self test switch.

G] Smoke sensor.

The smoke detector are modular units. There is a detector in each lavatory. The smoke detector uses 28vdc from the P18 panel.

The wheel well fire detection system detects high temperatures in the main wheel well and sends an alert to the flight crew.

These are the major components of the wheel well fire detection system:-

A] Wheel well fire detector elements.

B] Compartment overheat detection control module.

C] Overheat/Fire protection panel.

Detector elements in the main wheel well supply the wheel well fire detection signal. The signal goes to the compartment overheat detection control module. This module sends the fire alarm signal to the flight compartment.

The wheel well detector elements have these components:-

A] Nickel wire.

B] Insulation.

C] Electrical connector

D] Tube.

The detector element attaches to the ceiling of the wheel well by quick release fasteners.

The detector element is a thermistor type with resistance inversely proportional to temperature. As the element temperature rises, its resistance is lowered. If any portion of the sensing element is heated above alarm temperature, the element resistance drops sharply. The single wire in the center of the core is the power lead and the outside tube is electrically grounded. The insulating resistance of the core material decreases suddenly at the alarm temperature. Current flows through the core material to ground when the alarm temperature is sensed.

The minimum bend radius for the sensor element is one inch [2.5 cm]. If possible do not bend the element in a radius less than three inches [8 cm].

Detector element are in clamps with colour-coded bushings. The detector end brackets have collars that prevent the detector from twisting when the electrical connectors are put on.

DO NOT MAKE THE PERMITTED DENTS OR KINKS STRAIGHT. DAMAGE TO THE TUBING CAN OCCUR.

Make sure there is at least 0.50 inch [1.5 cm] between the element and the structure except at the mounting clips.

The Compartment Overheat detection control module front panel has these components:-

A] MAINT ADV light.

B] LED display.

C] BITE instructions.

D] Four BITE control switches.

The Compartment overheat detection control module is in the electronic equipment compartment on the E1-4 rack.

For normal conditions, the MAINT ADV light is off. When the light comes in, it shows there is a fault data stored in memory. The light stays on until you correct the problem and clear the memory. Use the BITE functions to find the fault or alarm condition.

These are the functions of the BITE control switches:-

A] LOC TEST switch starts a self test.

B] MEM READ switch shows the fault code for the last item kept in memory.

Push the OVHT/FIRE test switch to start a test of the wheel well fire detection system.

115vac power must be on to do a test of the Wheel well fire detection system.

These are the Flight compartment indications of a Wheel well fire:-

A] P8-1 WHEEL WELL light comes on.

B] P7 FIRE WARN light comes on.

C] P9 AURAL WARNING UNIT gives a bell sound.

To stop the bell sound, push one of these switches:-

A] P8 panel BELL CUTOUT push-button.

B] P7 panel FIRE WARN light.

C] P28 APU GROUND CONTROL panel.

If you have a wheel well fire alarm, the MAINT ADV light on the compartment overheat detection control module comes on.

The construction and operation of the wing/body overheat elements are similar to the wheel well elements. The alarm temperature set points are different for the wing and body overheat detection sense elements. Elements actuate at approximately 255 degF [124 degC] for these areas in the airplane.

A] Aft cargo compartment.

B] Right and Left air condition compartment.

C] Keelbeam.

Elements actuate at approximately 310 degF [154 degC] for these areas of the airplane

A] Engine strut cavities.

B] Wing Leading edge.

These are the indications of a wing/body overheat condition:-

A] Related P5 wing-body overheat light comes on.

B] P7 master caution and AIR COND lights come on.

C] MAINT ADV light comes on.

Push and hold the P5 OVHT TEST switch for 5 seconds to start a test of the wing and body overheat detection system. If the test is successful, the two p5 wing-body lights and the P7 MASTER CAUTION light come on.

The Lavatory fire extinguishing system extinguishes fires under the wash basin and trash bin areas.

The Lavatory fire extinguishing system has these components:-

A] Fire extinguisher bottle.

B] Temperature sensors.

C] Temperature indicator strip.

The extinguisher bottle has two discharge ports. The ports have eutectic plugs. These plugs melt at high temperatures, When there is an overheat or fire condition, this occurs:-

A] Temperature indicators change colour.

B] The eutectic plug melts.

C] The extinguisher releases inert gas to stop the fire.

There are two types of portable fire extinguishers:-

Halon extinguishers are for electrical and flammable liquids.

Water type extinguishers are for solid combustible fires.

There are portable extinguishers in these areas:-

A] Flight Compartment.

B] Galley.

C] Passenger compartment.

The Water-type extinguishers contain a water and anti-freeze mixture. Each water extinguisher has these ports:-

A] Trigger [discharge valve].

B] Water Cylinder.

C] Handle with internal gas cartridge.

D] Discharge nozzle.

E] Quick-release mounting strap.

Each Halon extinguisher has these parts:-

A] Pressure gage.

B] Halon cylinder.

C] Trigger.

D] Discharge nozzle.

E] Handle lock pin.

F] Handle.

To operate the water-type extinguisher, turn the handle and push the trigger.

To operate the Halon extinguisher, remove the handle lock pin and push the handle.

After you use the water-type extinguisher, you must fill it again and replace the cartridge.

If the handle lock pin on the halon extinguisher is not there, you must weigh the extinguisher to find out if it is not full. The pressure gage is not a satisfactory check of the extinguisher.